Saw blades for cutting semiconductor packages are well known. Such saw blades are made in the form of circular disc, gang saws and band saws. Circular saws may be made by bonding abrasives in a binder (to form so called solid resinoid blades) or by coating abrasives on a support disc (to form so called sintered blades). The outer periphery may be continuous or discontinuous. One of the purposes of providing discontinuities on the outer periphery cutting edge, in the form of slots, is to allow free passage for the outflow of particles abraded from the workpiece and associated coolant. The coolant is used to cool the saw blade as well as to flush particles or debris out of the blade.
These saws are employed in the semiconductor industry to separate individual packages one from another by cutting streets or separation channels into the packaging material. Typical diamond bonded saw blades have been made with a large range of thicknesses, for example, from about 25 microns up to about 500 microns.
Each separated package is then connected to a substrate. Numerous types of substrates are used that fall into a category of Surface Mounted Technology (or SMT) devices. A SMT packaged device may comprise a die mounted on a copper leadframe and encapsulated by a polymer molding with silica fillers. In addition, each SMT package has circuits on or interleaved therein with the circuits having metal laminates, test circuits, ground plane, etc. Each semiconductor package is therefore a composite of materials with different hardness, ductility and abrasiveness.
Some semiconductor packages are singulated using thick saw blades because of requirements for thicker or wider streets. Even these thick saw blades are also destroyed by the filler materials in the packages. They also clogged up rapidly with plastic and metals from the circuits. The clogged up blade then requires more force to make a cut, and cuts at a much slower rate because the diamonds that do the cutting are ineffective; in addition, there is often little room for the newly cut debris to be removed. The newly cut debris abrades the blade material causing excessive wear.
Saw blades of the solid type have a tendency to form a bullet-shaped profile edge after some use. This causes them to be rejected by the microelectronics industry because as the sides of the blades wore and the bottom of the blade becomes smaller and the semiconductor packages being cut grow directly with this wear. In consequence, the packages become wider and out of its dimensional specification. This means that the saw blades must be replaced relatively early before the blades are completely worn.
When clogged, these blades also have a tendency to make rough cuts which can smear or destroy the exposed circuit pattern, especially when the smear occurs at a conductive pad or bump on a substrate, in some cases, ripping them out altogether; these might cause electrical leakage between them. In addition, rough cut edges also tend to have burrs.
FIG. 1A shows a known cutting wheel 10. The wheel 10, as described in U.S. Pat. No. 3,628,292, has raised bosses 11 on one side, with each boss being formed exactly opposite a groove 12 on the other side. The area of the cutting bosses 11 is made equal to area of the grooves 12 and the effective thickness of the wheel 10 is maintained the same. The wheel 10 employs a resinoid binder of a mixture of ingredients using layers of mesh and grains of hard carbides. Similarly, FIG. 1B shows a known core drill 10a made with a ring of binder and abrasive particles.
With the push for increasing microelectronics processing and maintaining economic throughput, there is a need to increase microelectronics singulating speeds yet giving each packaged device clean cut edges. A clean cut edge or surface has minimal edge chipping, inter-layer chipping, metal burrs and metal smearing. Despite development in thin-wall abrasive impregnated saws, there is a need for a new higher performance saw.